The present invention relates to a shockproof device for a power generator with an oscillating weight, intended to protect the moving elements of the device against any damage, in particular in the event of shocks able to cause excessive oscillation of said oscillating weight liable to cause irreversible damage to the elements and wheels an pinions in the kinematic chain meshed with a mechanical energy accumulator such as a barrel, or with the rotor of an electric generator.
The invention concerns, in particular, a device of this type for a power generator of small dimensions with an oscillating weight, whose moving elements are naturally more fragile, said generator being used to activate an instrument of small volume carried by a user whose movements will cause the oscillating weight to oscillate. It concerns, for example, in a non-limiting way, a wristwatch whose electronic movement and/or electronic circuit for transmitting and/or receiving electromagnetic signals, is powered directly or indirectly by the current generated by an electric microgenerator driven by the oscillating weight.
It has long been sought to resolve the problems of mechanical resistance posed by power generators with an oscillating weight in the event of misuse, shock, or accidental dropping of the apparatus, and a certain number of solutions have already been proposed.
For mechanical self winding watches, Swiss Patent No. 281 490, published in 1952, discloses a timepiece including an oscillating winding weight supported by a thin elastic zigzagged arm, intended to dampen any axial shocks borne by the weight. This arm is secured to a pinion meshing with a toothed sector which co-operates with the barrel ratchet wheel, the assembly being completed by two shock absorber springs which limit the amplitude of the oscillations of the weight.
According to an earlier document, Swiss Patent No. 254 577 published in 1948, shock absorption or dampening of the oscillating weight is obtained by means of a spiral spring with a vertical strip mounted between the oscillating weight and a part secured with the pivots. According to one embodiment, this spiral spring surrounds the pivoting arbour of the oscillating weight and according to another embodiment one or more of these springs are arranged above the oscillating weight, while being off-centre with respect to said pivoting arbour to form an elastic connection between a bell secured to the pivoting arbour and the oscillating weight itself. In this construction it will be noted that the ends are securely anchored to their respective points of attachment by means of pins and that overshooting the dampening limits could cause deformation of the spring without however removing it from its anchoring points.
In a more recent document, European Patent No. 0 791 867, a device is proposed wherein, according to one embodiment, dampening is obtained by means of an intermediate wheel and pinion formed by a toothed wheel supporting a flat spiral coiled spring having at most three turns, whose ends are securely anchored on the one hand, in said wheel, meshed with the pinion of the generator rotor, and on the other hand in an arbour able to freely rotate in said wheel, said arbour including a pinion meshed with the teeth of a ring supporting the oscillating weight. In normal operation, the spiral coiled strip has sufficient rigidity that it undergoes practically no deformation. When the oscillating weight is driven more than normally, for example during an abrupt movement for a watch worn on the wrist, the flat spiral coiled spring can certainly be deformed sufficiently to avoid damaging the gear trains.
For more significant stress on the oscillating weight, for example when the instrument of small volume is dropped, the flat spiral spring mountings will probably resist. However, there is certainly a risk that the flat spiral spring will buckle creating irreversible deformation, which is detrimental to the operation of the instrument.
In order to overcome the inadequacies or drawbacks which still exist in the most pertinent devices of the aforecited prior art to avoid damage created by the oscillating weight operating in extreme conditions, the present invention concerns a shockproof device in which the arrangement of a spiral coiled spring wound in a micro-barrel both prevents an anchoring point of the spring being torn off or the irreversible deformation thereof when the oscillating weight is made to move in extreme conditions, and provides a small reserve of inertia favourable to the global efficiency of the device in such conditions.
The invention thus concerns a shockproof device for a generator activated by the alternating movements of an oscillating weight transmitted to the generator via a barrel, said generator including a rotor provided with a pinion, said oscillating weight including an unbalanced mass secured to an axle and supported by a toothed ring, and said barrel including a drum, having a base extended radially by a ring to form a toothed wheel, which rotates freely about a pivoted arbour and inside which is wound a spiral coiled spring coupled by one end to the oscillating weight axle and secured by the other end to the inner wall of the drum to form driving means for the rotor, said spiral coiled spring having an elastic constant, such that during normal operation, the turns are wound or unwound from a neutral position in which they are regularly spaced and occupy, in the event of a shock, an open position in which the turns are pressed against the inside of the drum or a closed position in which the turns are regrouped at the centre, characterised in that a sliding strip is also coupled to the arbour driven by the oscillating weight wound in the same manner as the spiral coiled spring to surround the latter without any rigid mechanical connection over a length substantially corresponding to a turn in an open position.
The shockproof device according to the invention may be formed of a single mechanical entity including both the barrel and the oscillating weight. In this embodiment, the unbalanced mass of the oscillating weight is mounted so as to rotate freely with respect to the toothed ring. The barrel and the oscillating weight have the same axis of revolution, so that the barrel arbour and the oscillating weight axle form a single part. Likewise, the toothed wheel of the barrel and the toothed wheel of the oscillating weight form a single part to form a single toothing which meshes directly with the rotor pinion.
According to another preferred embodiment of the invention, the shockproof device according to the invention is made in the form of an intermediate wheel and pinion inserted between the generator and the oscillating weight. This intermediate wheel and pinion includes a barrel, as defined previously, whose toothed wheel meshes with the rotor pinion and whose arbour is extended by a pinion which meshes with the toothed ring of the oscillating weight whose unbalanced mass is secured to said ring, for example by being made integral therewith, by being welded or forced thereon. This embodiment, which will be taken as an illustrative example hereinafter, has the advantage, compared to the preceding embodiment, of reducing the global height of the device and increasing the rotor speed as a result of a step up gear.
This device wherein alternating mechanical energy is transformed into a direct current, obviously includes in a known manner a mechanical inversion system such as a click wheel, allowing the rotor always to be driven in the same direction, or an electronic polarity inverting circuit.